**1. Introduction**

### **1.1 General information about** *cork taint* **and TCA in wine**

The problem of *cork tainted* wines has been known to winemakers for a long time, but in the second half of the twentieth century, it began to attract more and more attention [1–3]. The origin of this problem was not well understood until the 1970–80s, before works on 2,4,6-trichloroanisole (TCA) and its contribution to the *cork taint* were published [4–6]. Now it is well known that TCA can migrate from cork stoppers and contaminate wine during bottle storage. Moreover, it was discovered that TCA is a widespread pollutant, which has also been found in various food products (coffee, poultry, etc.) as well as in water for public consumption.


#### **Table 1.**

*Sensory threshold levels for TCA in wine (adopted from [7] and modified).*

TCA causes sensory defects, which are usually described as musty, moldy, and wet cardboard off-odors. The situation with TCA contamination is particularly challenging because even trace amounts of this compound can lead to sensory problems in foods. Peculiarly, the human olfactory system is extremely sensitive to TCA molecules. In the case of wine, TCA sensory threshold levels are often about 1.4–1.5 ng/L (**Table 1**) or lower (especially for white or sparkling wines) and typically vary up to 3–4 ng/L. Generally, the variations in sensory threshold values occur due to the following factors:

*Wine matrix*. First, the ethanol content in wine increases TCA threshold levels (in comparison, TCA sensory thresholds in water are much lower, starting from about 0.03 ng/L [16]). Second, the overall wine aroma intensity has a masking effect on the TCA perception. Therefore, TCA sensory thresholds are higher for wines made from aromatic grape varieties. In addition, TCA is usually better masked in red wines, as their aroma composition is often more intense compared with white wines. Woody notes in wine can also mask TCA defects, especially in the case of white wines [7].

*Personal characteristics of tasters.* The sensitivity of people to TCA can vary significantly depending on their olfactory system particularities, the current physiological state of sense organs [17], as well as their experience and training. Thus, the knowledge of "*cork taint*" has been found to be negatively correlated with individual TCA detection thresholds, i.e., awareness about *cork taint* increases the sensitivity of tasters to TCA [10].

*Mode of sensory evaluation*. Comparison of orthonasal (smell) and retronasal (volatiles traveling from the mouth into the nasal cavity) approaches shows that the latter usually provides a higher sensitivity to TCA. This effect is explained by the increased volatility of aroma substances at higher temperatures in the mouth. Another aspect of sensory evaluation is related to the tasters' attitude toward the perceived TCA smell. For example, it was shown that wine consumers could detect TCA at a concentration of 2.1 ng/L in the wine (detection threshold) and tolerate it, while for the consumer rejection threshold, the TCA content had to reach the level of 3.1 ng/L [10].

*Fatigue and suppression of olfactory receptors.* Already after a short exposure of tasters to *cork tainted* wines, their sensitivity to TCA drops rapidly and significantly (fatigue/adaptation effects). The mechanism of TCA interaction with olfactory system is not thoroughly studied. Nevertheless, TCA has been shown to attenuate olfactory transduction, which can lead to the suppression of wine aromas in general [18]. Moreover, such suppression was observed even at extremely low TCA concentrations, which are below the defined sensory thresholds. The masking of certain

*State-of-the-Art Knowledge about 2,4,6-Trichloroanisole (TCA) and Strategies to Avoid… DOI: http://dx.doi.org/10.5772/intechopen.103709*

wine notes by infra-threshold TCA concentrations (0.1–1 ng/L) was demonstrated for various wines [19–21].
